[42.04] The Third EGRET Catalog of High Energy Gamma Ray Sources

R. C. Hartman (NASA/GSFC), EGRET Team

The Third EGRET Catalog has been accepted for publication in
the ApJ Supplements. Its covers CGRO Cycles 1-4 (1991 April
22 to 1995 October 3), the entire time that EGRET operated
in its normal wide-field-of-view mode. The Catalog contains
271 sources, a substantial increase over the sum of the
Second Catalog (Thompson et al. 1995 - 2EG) and the Second
Catalog Supplement (Thompson et al. 1996 - 2EGS). This is
due to the inclusion of Cycle 4 (not covered in 2EG or
2EGS), use of maps of the summed data for the entire time
period as well as those for individual observations, and use
of a slightly different analysis technique that decreases
the source detection threshold somewhat. The 271 sources in
the catalog include one solar flare, six gamma-ray pulsars,
the Large Magellanic Cloud, one possible detection of a
radio galaxy (Cen A ), 67 strong identifications of blazars
and flat-spectrum radio sources, and 27 possible blazar
detections. There are 169 unidentified sources, 79 of them
within 10 degrees of the Galactic plane. The "cloud" of
apparent sources within 30 degrees of the Galactic Center,
seen in 2EG+2EGS, is even more obvious in this catalog; it
appears to be somewhat more dense to the north of the
Galactic plane.